diff --git a/pillar/web/utils/forms.py b/pillar/web/utils/forms.py
index c7dd85b5..c38abcd6 100644
--- a/pillar/web/utils/forms.py
+++ b/pillar/web/utils/forms.py
@@ -181,7 +181,7 @@ class JSONRequired(validators.DataRequired):
         try:
             json.loads(field.data)
         except ValueError as ex:
-            message = self.message or ex.message
+            message = self.message or str(ex)
 
             field.errors[:] = []
             raise validators.StopValidation(message)